The use of a tympanic membrane thermometer for assessing hyperthermia in bighorn sheep

In November 1992, 45 desert bighorn sheep (Ovis canadensis nelsoni) were captured at Old Dad Peak and the Kelso Mountains of southern California (USA) using a netgun fired from a helicopter. Tympanic membrane temperature was compared to rectal temperature for 22 sheep to determine if tympanic membrane temperature was a reliable indicator of hyperthermia and capture stress. All animals captured had elevated rectal temperatures after capture and arrival to the processing area. The group of 22 sheep had a mean +/- SD rectal temperature of 40.9 +/- 0.7 C (range 39.5 to 42.1 C) at arrival. During processing of these sheep, mean +/- SD rectal temperatures were 40.9 +/- 0.29 C (range 40.0 to 41.7 C) with mean +/- SD tympanic temperatures of 38.4 +/- 0.5 C (range 35.7 to 40.5 C). Mean tympanic temperatures were significantly lower than mean rectal temperatures when comparing all measurements and paired tympanic and rectal temperature measurements. Three animals had rectal and tympanic temperatures greater than 41.0 C and 39.7 C, respectively, one of which died after capture. Tympanic membrane temperature measurement may provide a method for evaluation of hyperthermia and capture stress by separating retained body heat due to exertion from critical elevations in core body temperature which may affect post-capture survival.